Vehicle control

ABSTRACT

A vehicle control system has a plurality of subsystem controllers including an engine management system 28, a transmission controller 30, a steering controller 48, a brakes controller 62 and a suspension controller 82. These subsystem controllers are each operable in a plurality of subsystem modes, and are all connected to a vehicle mode controller 98 which controls the modes of operation of each of the subsystem controllers so as to provide a number of driving modes for the vehicle. Each of the modes corresponds to a particular driving condition or set of driving conditions, and in each mode each of the functions is set to the function in mode most appropriate to those conditions.

More than one reissue application has been filed for the reissue of U.S.Pat. No. 7,349,776. The reissue application numbers are Ser. Nos.15/277,516 and 15/949,385 (the present application), which is acontinuation reissue application of application Ser. No. 15/277,516.

BACKGROUND OF INVENTION

1. Field of the Invention

The present invention relates to the control of vehicles, in particularto the coordinated control of a number of subsystems of a vehicle.

2. Background Art

Various systems are known in which operation of various subsystems of avehicle can operate in different configuration modes so as to suitdifferent conditions. For example, automatic transmissions can becontrolled in sport, winter, economy and manual configuration modes inwhich the changes between gear ratios and other subsystem controlparameters are modified so as to suit the prevailing conditions or thetaste of the driver. Air suspensions are known with on-road and off-roadconfiguration modes. Stability control systems can be operated atreduced activity so as to give the driver more direct control over theoperation of the vehicle. Power steering systems can be operated indifferent configurations modes where the level of assistance is atdifferent levels or varies in different ways. Vehicle transmissions canbe switched to provide drive to different numbers of wheels. Also thelocking or partial locking of differentials can be controlled to suitthe prevailing driving conditions.

As the number of controllable systems increases, the driver will becomefaced with an increasing number of choices as to which configurationmodes to select for each of the systems. Unless the driver is veryexperienced, this can become complicated and confusing.

Therefore, systems have been proposed in which the control of a numberof the vehicle subsystems is coordinated by a central vehiclecontroller, which can be switched between a number of modes therebycontrolling all of the subsystems in a coordinated way which is simplefor the driver to control. Such a system is disclosed in GB2273580.

While GB2273580 teaches an integrated control system to control andconfigure vehicle operating subsystems in response to control signals,drivers often encounter a broad range of surfaces and terrains in bothon-road and off-road settings. Unfortunately, the operatingcharacteristics of such an integrated control system does not providethe driver with the ability to provide direct input regarding thesurface terrain in an attempt to better select the appropriate subsystemconfiguration modes. This deficiency results in the less than optimalstability, handling, and safety performance of the vehicle. Therefore,to further expand the performance of motor vehicles including integratedcontrol systems as noted above, there is a need for an integratedcontrol system which will provide improved control of the vehicle on abroad range of surfaces.

SUMMARY OF INVENTION

The present invention aims to provide a vehicle control system which canbe operated so as to provide improved control of the vehicle on abroader range of surfaces, and in particular in a plurality of differentoff-road surfaces and terrains such as might be encountered when drivingoff-road.

Accordingly the present invention provides a vehicle control systemarranged to control a plurality of vehicle subsystems each of which isoperable in a plurality of subsystem configuration modes, wherein thevehicle control system is operable in a plurality of driving modes ineach of which it is arranged to select the subsystem configuration modesin a manner suitable for a respective driving surface.

Preferably each of the subsystems is operable in a plurality ofsubsystem configuration modes and in each of the driving modes thesubsystem configuration modes are selected in a manner suitable fordriving on the respective surface.

Preferably one of the subsystems comprises a suspension system and saidplurality of subsystem configuration modes comprises a plurality of rideheights.

Preferably one of the subsystems comprises a fluid suspension system inwhich fluid interconnection can be made between suspensions for wheelson opposite sides of the vehicle, and said plurality of subsystemconfiguration modes provide different levels of said interconnection.

Preferably one of the subsystems comprises a steering system which canprovide steering assistance, and said plurality of subsystemconfiguration modes provides different levels of said steeringassistance.

Preferably one of the subsystems comprises a braking system which canprovide braking assistance, and said plurality of subsystemconfiguration modes provides different levels of said brakingassistance.

Preferably one of the subsystems comprises a brake control system whichcan provide an anti-lock function to control wheel slip, and saidplurality of subsystem configuration modes allow different levels ofsaid wheel slip.

Preferably one of the subsystems comprises a traction control systemwhich is arranged to control wheel spin, and said plurality of subsystemconfiguration modes allow different levels of said wheel spin.

Preferably one of the subsystems comprises a yaw control system which isarranged to control vehicle yaw, and said plurality of subsystemconfiguration modes allow different levels of divergence of said vehicleyaw from an expected yaw.

Preferably one of the subsystems comprises a range change transmissionand said subsystem configuration modes include a high range mode and alow range mode of said transmission.

Preferably one of the subsystems comprises a powertrain system whichincludes a powertrain control means and a throttle pedal, the subsystemconfiguration modes providing different levels of responsiveness of thepowertrain control means to movement of the throttle pedal.

Preferably one of the subsystems comprises a transmission systemoperable in a plurality of transmission ratios and including atransmission control means arranged to monitor at least one parameter ofthe vehicle and to select the transmission ratios in response, andwherein the subsystem modes include a plurality of transmissionconfiguration modes in which the transmission ratios are selecteddifferently in response to said at least one parameter.

Preferably one of the subsystems comprises a differential systemoperable to provide a plurality of levels of differential lock, and thesubsystem configuration modes are arranged to provide different levelsof said lock.

Preferably the differential system is arranged to control the level ofdifferential lock on the basis of a plurality of inputs, and to responddifferently to said inputs in each of the modes.

The differential may be a center differential, a front differential, ora rear differential.

Preferably one of the subsystems comprises a roll control systemarranged to provide roll correction to reduce vehicle roll and thesubsystem configuration modes provide different levels of rollcorrection of the vehicle, at least under some driving conditions.

Preferably one of the subsystems is a speed control system arranged tocontrol the speed of the vehicle when descending a hill. The speedcontrol system may be arranged to control the vehicle to differentspeeds in the different configuration modes.

Preferably the driving modes include an off-road mode in which thesubsystems are controlled in a manner suitable for driving on roughterrain and an on-road mode in which the subsystems are controlled in amanner suitable for driving on-road.

Preferably the suspension system is arranged to provide a higher rideheight in the off road mode than in the on-road mode.

Preferably in the off-road mode a higher level of said interconnectionis provided than in the on-road mode.

Preferably the traction control system is arranged to allow less wheelspin in the off-road mode than in the on-road mode.

Preferably the yaw control system is arranged to allow a higher degreeof said divergence in the off-road mode than in the on-road mode.

Preferably in the off-road mode the range change transmission isoperated in the low range.

Preferably in the off-road mode the powertrain control means is arrangedto provide lower levels of drive torque, for a given throttle pedalposition, at least at low levels of throttle pedal depression, than inthe on-road mode.

Preferably the differential system is arranged to provide higher levelsof differential lock in the off-road mode than in the on-road mode.

Preferably the roll control system is arranged to provide a higher rollstiffness in the on-road mode than in the off-road mode.

Preferably the speed control system is arranged to be switched on in theoff-road mode and switched off in the on-road mode.

Preferably the driving modes include at least one low friction mode inwhich the subsystems are controlled in a manner suitable for driving onlow friction surfaces and a high friction mode in which the subsystemsare controlled in a manner suitable for driving on high frictionsurfaces.

Preferably the brake control system allows higher levels of slip in thehigh friction mode than in the low friction mode.

Preferably the traction control system allows higher levels of wheelspin in the high friction mode than in the low friction mode.

Preferably the braking control system provides a greater level ofbraking assistance in the high friction mode than in the low frictionmode.

Preferably the powertrain control means is arranged to provide lowerlevels of drive torque, for a given throttle pedal position, at least atlow levels of throttle pedal depression, in the low friction mode thanin the high friction mode.

Preferably the transmission system is arranged to operate in highergears for a given value of said at least one parameter in the highfriction mode than in the low friction mode.

Preferably the differential system is arranged to provide higher levelsof differential lock in the low friction mode than in the high frictionmode.

The high friction mode may comprise a standard or default mode in whichthe vehicle will operate normally and which is suitable for on-roaddriving.

Preferably there are two such low friction modes and the suspensionsystem is arranged to provide a higher ride height in one of the lowfriction modes than in the other.

Preferably there are two such low friction modes and the suspensionsystem is arranged to provide a higher level of said cross linking inone of the low friction modes than in the other.

For example the two low friction modes may comprise a mud mode suitablefor traveling through deep mud, and another low friction mode suitablefor driving in snow, on grass, or on gravel.

Alternatively there may be a plurality of low friction modes, one ofwhich may be a grass mode in which the subsystems are controlled in amanner suitable for driving on grass, one of which may be an ice mode inwhich the subsystems are controlled in a manner suitable for driving inice, and one of which may be a mud mode in which the subsystems arecontrolled in a manner suitable for driving on mud.

Preferably one of the modes is a sand mode in which the subsystems arecontrolled in a manner suitable for driving on sand. Preferably at leastone of the subsystems is arranged, in the sand mode, to allow onlyrelatively low levels of wheel spin when the vehicle is traveling at lowspeeds so as to avoid the vehicle wheels becoming submerged in sand, butto allow relatively high levels of wheel spin when the vehicle istraveling at higher speeds.

Preferably the powertrain control system is arranged to providerelatively low levels of drive torque for a given throttle pedalposition at low vehicle speeds and to provide relatively high levels ofdrive torque for a given throttle pedal position at higher vehiclespeeds.

The off-road mode may be a rock crawl mode in which the subsystems arecontrolled in a manner suitable for driving over rocks. Alternatively itmay be set up for more general off-road use.

One of the modes may be a rough-road mode in which the subsystems arecontrolled in a manner suitable for driving on rough roads, for examplefor driving at relatively high speeds over rough surfaces.

At least one of the modes may be a plough surface mode in which thebrake control subsystem is arranged to allow a relatively high degree ofwheel slip under braking. This is useful, for example on snow or sand,where the build up of matter in front of the wheels under braking canimprove braking performance.

Preferably at least one of the modes is an on-road mode in which thesubsystems are controlled in a manner suitable for driving on-road. Forexample, one of the modes may be a motorway mode in which the subsystemsare controlled in a manner suitable for driving at high speed on a flatroad surface, or one of the modes may be a country road mode in whichthe subsystems are controlled in a manner suitable for driving oncountry roads.

The driving modes may be selectable by means of two inputs, one of whichis a terrain selection input arranged to influence the mode selected onthe basis of the terrain selected, and the other which is a mode of useinput arranged to influence the mode selected on the basis of a selectedmode of use of the vehicle. Each of these inputs may be user-controlledinputs, or may be derived from one or more sensors.

The mode of use input may be arranged to allow selection between aplurality of driving styles, which may include, for example, a normalstyle, a sport style, and an economy style.

Alternatively, or in addition, the mode of use input may be arranged toallow selection between a plurality of states of the vehicle, forexample including a towing state or a loaded state.

The present invention further provides a vehicle comprising a systemaccording to the invention and said plurality of subsystems. Preferredembodiments of the present invention will now be described by way ofexample only with reference to the accompanying drawings and theappended claims.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagrammatic representation of a powertrain subsystem of avehicle according to an embodiment of the invention;

FIG. 2 is a diagrammatic representation of steering and brakessubsystems of the vehicle of FIG. 1;

FIG. 3 is a diagrammatic representation of a suspension subsystem of thevehicle of FIG. 1;

FIG. 4 is a diagrammatic representation of a vehicle mode controllercontrolling the subsystems of FIGS. 1 to 3;

FIGS. 5 and 6 make up a table showing operation of the vehicle modecontroller of FIG. 4;

FIG. 7 is a graph showing throttle characteristics in a secondembodiment of the invention;

FIGS. 8 and 9 are graphs showing control of differentials forming partof the second embodiment;

FIG. 10 is a graph showing traction control characteristics in thesecond embodiment

FIG. 11 is a graph showing yaw control characteristics in the secondembodiment;

FIG. 12 is a graph showing control of the differentials of the secondembodiment;

FIG. 13 shows user inputs forming part of a third embodiment of theinvention;

FIG. 14 is a diagrammatic representation of a powertrain subsystem of avehicle according to a fourth embodiment of the invention; and

FIG. 15 is a diagrammatic representation of part of a suspensionsubsystem of the vehicle according to the fourth embodiment of theinvention.

DETAILED DESCRIPTION

Referring to FIG. 1, according to a first embodiment of the invention avehicle 10 has four wheels 11, 12, 13, 14 and a powertrain 16 forproviding driving torque to the wheels. The powertrain 16 comprises anengine 18, an automatic transmission 20 which transmits drive torque atany of a number of transmission ratios, via a transfer box 21 to theinput side of a center differential 22. Front and rear differentials 24,26 receive torque from the center differential 22 and transmit it to thefront wheels 11, 12 and rear wheels 13, 14 respectively. An enginecontroller 28 in the form of an engine management system controlsoperation of the engine 18 so as to control its speed and output powerand torque in response to inputs from the driver from a throttle pedal27, the position of which is measured with a throttle pedal positionsensor 29. A transmission controller 30 controls the transmission ratioof the automatic transmission 20, and the selection of high or low rangein the transfer box 21. It also controls the center differential 22 soas to control the distribution of drive torque between the front andrear axles, and the rear differential 26 so as to control thedistribution of drive torque between the two rear wheels 13, 14. Thetransmission controller 30 could also control the distribution of drivetorque between the front two wheels 13, 14.

Referring to FIG. 2, the vehicle further comprises a steering system 40for steering the front wheels 11, 12, and a brake system 50 for brakingall four wheels 11, 12, 13, and 14. The steering system 40 comprises asteering wheel 41, a steering column 42 for transmitting steering inputtorque input by the driver to the steering wheel to pinion 43 of a rackand pinion steering system. The pinion 43 transmits the steering torqueto a rack 44, which is connected to steering arms 45 by means of whichit applies a steering force to the steering knuckles 46 of the frontwheels to steer them. A PAS (power assisted steering) motor 47 appliessteering forces to the rack 44 to assist the driver in steering thevehicle, under the control of a steering controller 48 which receivesinputs from a steering angle sensor 49, which measures the steeringangle of the steering wheel 41.

The brake system 50 comprises a brake disk 51, 52, 53, 54, and a brakecaliper 55, 56, 57, 58 for each of the wheels each of which is actuatedhydraulically from a hydraulic brake control block 60. The hydrauliccontrol block 60 controls the hydraulic pressure and hence the brakingtorque at each wheel under the control of a brake controller 62 whichreceives wheel speed signals from wheels speed sensors 63, 64, 65, 66 ateach of the wheels. A driver operated brake pedal 67 provides via amaster cylinder the driver input to the brake system 50 and createshydraulic pressure to operate the brakes at a first inlet port 60a tothe control block 60, with the assistance of a brake booster 68. Thebooster 68 is also controlled by the controller 62 so as to vary theamount of assistance provided by the brake booster 68 and therefore thelevel of braking effort required from the driver to produce anyparticular level of braking torque at the wheels. A pump 60b is alsoprovided which can provide hydraulic pressure to actuate the brakesindependently of the brake pedal. The pump 60b is also controlled by thecontroller 62. Brake fluid is returned to a reservoir 60c on return fromthe brake calipers 55, 56, 57, and 58 from where it is supplied to thepump 60b or the master cylinder operated by the brake pedal 67. Thebrake controller 62 also receives an input from a yaw sensor 69 whichmeasures the yaw rate of the vehicle.

Referring to FIG. 3, the vehicle further comprises a suspension system70 which includes an active air suspension system 72 and an active rollcontrol system 74. The active air suspension system 72 comprises an airspring 76, 77, 78, 79 at each wheel, and a valve block 80 which controlsthe ride height of each of the wheels 11, 12, 13, 14 and the springrates of the air springs 76, 77, 78, 79 by controlling the air pressurein each of the air springs, the supply of air under pressure to each ofthe air springs and the release of air from the air springs. The valveblock 80 further controls the degree to which the two front air springs76, 77 are interconnected, the degree to which the rear air springs 78,79 are interconnected, and the degree to which the front air springs 76,77 are interconnected to the rear air springs 78, 79. The valve block 80is controlled by an air suspension controller 82 which receives rideheight signals from ride height sensors 83, 84, 85, 86 arranged tomeasure the ride height of each of the wheels 11, 12, 13, 14. Thesuspension controller 82 can also measure the air pressure in each ofthe air springs 76, 77, 78, 79 using a pressure sensor 88 in the valveblock 80, as well as the lateral acceleration of the vehicle using alateral accelerometer 89.

The active roll control system 74 comprises a front anti-roll bar 90which is connected between the two front wheels 11, 12 and acts toresist roll of the front of the vehicle, and a rear anti-roll bar 92which is connected between the two rear wheels 13, 14 and acts to resistroll of the rear of the vehicle. Each of the anti-roll bars 90, 92 is intwo halves with a rotary actuator 94, 96 acting between the two halves.These roll control actuators can actively increase (or decrease) theresistance to roll provided by the anti-roll bars by applying a rollcorrection torque under the control of the suspension controller 82.They can therefore control the roll stiffness of the vehicle.

Within the systems described above there are various functions which canbe controlled in different ways depending on the prevailing drivingconditions. These functions will now be described.

The suspension system 70 is adjustable between a plurality of rideheights. In this case there are three possible ride heights: “high”which is suitable for off-road driving; “low” which is suitable for highspeed driving, for example on motorways, where a low wind resistance isrequired; and “standard” which is between the “high” and “low” settingsand is suitable for most normal on-road driving.

The interconnection between air springs of the active air suspensionsystem 72 on opposite sides of the vehicle is variable between an “open”condition where there is interconnection between the two sides of thevehicle, and “closed” where there is no interconnection. In the “closed”condition the roll stiffness of the vehicle is increased, and so is theoverall spring rate of the suspension. This therefore makes the vehiclemore suitable for driving on smooth surfaces at higher speeds. In the“open” condition the roll stiffness is decreased, but the suspension canarticulate more easily, making it more suitable for driving on roughersurfaces and at lower speeds. The interconnection valves are normallykept in the closed condition to provide high roll stiffness andstabilize the vehicle. Under certain conditions when there is a lot ofvertical wheel travel the interconnection valves are opened to reduceresistance to this travel. However the system also needs to close theinterconnection at high vehicle speeds to stabilize the vehicle becauseopening the interconnection reduces resistance to roll as well asresistance to articulation. The system can be varied to vary the amountof wheel travel that is required to cause opening of the interconnectionvalves, so that the interconnection will open more or less easily, andto vary the vehicle speed above which the interconnection will be keptclosed. The system has three settings: standard, medium and maximum. Inthe standard setting the interconnection will happen up to quite highspeeds, of about 50 kph but only at quite high levels of articulation.In the medium setting the interconnection will occur only at lowerspeeds, but also at lower levels of articulation. In the maximum settinginterconnection will occur only up to low speeds, of about 15 kph, butat even lower levels of articulation.

The brake pedal effort is controllable according to a plurality of, inthis case two, basic characteristics. These are “high” and “low”requiring relatively high and low levels of braking effort from thedriver. However further brake control functions can also be added tothese basic characteristics under certain circumstances. For example a“panic assist” function detects very rapid brake pedal depressionindicative of emergency braking and provides an increased level ofbraking assistance in response.

The brake controller 62 provides an ABS (anti-lock) function which isalso operable in a number of different configuration modes. There is a“high mu” mode for use on surfaces with a high coefficient of friction.In this mode a relatively high level of slip is allowed to maximizedeceleration rates. There is also a “low mu” mode in which only muchlower levels of slip are allowed so as to ensure that good control overthe vehicle will be maintained at all times. Finally there is also a“plough” mode which is designed for surfaces, such as sand and snow, inwhich a barrier of matter will build up in front of a wheel which isslipping under braking. In this mode higher levels of slip are allowedeven than in the “high mu” mode to take advantage of the braking effectof the build up of material in front of the wheels.

The brake controller 62 and the engine management system 28 also providean E.T.C. (electronic traction control) function in which the brakes areapplied using the pump 60b to counteract wheel spin caused by thepowertrain 16 applying more torque to one or more of the wheels than canbe transmitted through the tires to the ground. The detection of wheelspin is carried out using the wheel speed sensors 63, 64, 65, 66. Ifjust one of the wheels is spinning, then that wheel is braked under thecontrol of the brake controller 62. If enough of the wheels are spinningto indicate that the overall drive torque is too high for the surface onwhich the vehicle is traveling, the engine management system 28intervenes to reduce the overall power output of the engine 18, therebyreducing wheel spin and maintaining traction. The E.T.C. function has“high mu” and “low mu” modes which, in similar manner to the A.B.S.function, allow higher and lower degrees of wheel spin, or slip, toallow more aggressive driving on higher friction surfaces, but maintaincontrol on lower friction surfaces.

The E.T.C. function also has a sand mode which keeps wheel spin low atlow speeds, following the “low mu” mode, to prevent the wheels fromdigging into the sand, but allows more spin at higher speeds, followingthe “high mu” mode because at higher speeds on sand higher levels ofwheel spin are less of a problem and can even improve traction.

The brake controller 62 also provides a D.S.C. (dynamic stabilitycontrol) function. This function monitors the vehicle speed and thesteering angle using the wheel speed sensors 63, 64, 65, 66 and thesteering angle sensor 49 and determines the expected yaw rate of thevehicle. This is compared with the actual yaw rate as measured by theyaw sensor 69, and the brakes are applied at individual wheels tocontrol the vehicle yaw if it starts to deviate in an undesirable wayfrom the expected yaw. Braking one or more of the outside wheels on acorner helps to neutralize oversteer, and braking one or more of theinside wheels on a corner helps to neutralize understeer. This functionalso has “high mu” and “low mu” modes in which the level of yawdeviation allowed is relatively high and relatively low respectively.

The throttle pedal characteristic, which relates the amount of torqueprovided by the engine 18 to the position of the throttle pedal 27, cantake a number of different forms. These include “quick” characteristicwhich is highly progressive, causing the torque to increase rapidly atlow degrees of pedal displacement and then to increase more slowly athigher degrees of pedal displacement, and a “slow” characteristic inwhich the torque increases more slowly at lower levels of pedaldisplacement and more quickly at higher levels of pedal displacement. Inan alternative to this type of arrangement the throttle pedalcharacteristic may relate the vehicle speed directly to the throttlepedal position. In this case the rate at which vehicle speed varies withthrottle pedal position can be varied between more and less progressivecharacteristics.

The transfer box 21 can be shifted between a “high range” and a “lowrange” to select the range of gear ratios most suitable to theprevailing conditions in known manner.

The automatic transmission 20 has a number of configuration modes eachof which defines when shifts between gears will take place, in responseto changes in throttle pedal position, vehicle speed, engine speed,engine torque and throttle pedal position, and some other factors whichare occasionally relevant such as gearbox temperature and ambienttemperature. There is a “normal” mode which provides a reasonablecompromise between fuel economy and driving performance, a “performance”which generally keeps the transmission in lower gears than in the normalmode, particularly when the driver is requesting a high level of drivingtorque to accelerate the vehicle, and a “manual” mode in which thecontrol of gear changes is given completely to the driver. There is alsoan “ice” mode which generally keeps the transmission in higher gearsthan the normal mode, in particular under acceleration from rest, toavoid loss of traction due to wheel spin, and a “sand” mode which keepsthe transmission in relatively high gears at low speed to avoidexcessive wheel spin which can result in the wheels digging themselvesinto the sand, but uses relatively low gears at higher speeds where arelatively high degree of wheel slip can be desirable to provide maximumtraction, and lower gearing helps the engine 18 to remain in anoperating region where the engine speed is high and the power output ishigh, thereby helping to avoid the vehicle becoming “bogged down” by alack of power.

The center differential 22 and the rear differential 26 each include aclutch pack and are controllable to vary the degree of locking between a“fully open” and a “fully locked” state. The actual degree of locking atany one time is controlled on the basis of a number of factors in aknown manner, but the control can be adjusted so that the differentialsare “more open” or “more locked”. Specifically the pre-load on theclutch pack can be varied which in turn controls the locking torque,i.e. the torque across the differential that will cause the clutch, andhence the differential, to slip. The front differential could also becontrolled in the same way.

Referring to FIG. 4, all of the subsystem controllers, that is theengine management system 28, the transmission controller 30, thesteering controller 48, the brakes controller 62 and the suspensioncontroller 82 are all connected to a vehicle mode controller 98 whichcontrols the configuration modes of operation of each of the subsystemcontrollers. In one example, the vehicle mode controller 98 stores inputregarding driving conditions in its memory and provides the appropriatecontrol commands to each subsystem controller. The subsystems, and eachof the functions described above, are controlled so as to provide anumber of driving modes for the vehicle. Each of the driving modescorresponds to a particular driving condition or set of drivingconditions, and in each driving mode each of the functions is set to thefunction mode most appropriate to those conditions.

The driving modes are selected by means of a driver input 99 which takesthe form of a rotary knob which can be rotated by the driver to selectany of the driving modes displayed as being available. As an alternativeto this rotary knob a touch screen, or a number of push buttons, one foreach driving mode, could be used.

Referring to FIGS. 5 and 6, the driving modes include three on-roadmodes, namely a motorway mode, a country road mode and a city drivingmode, four off-road modes, namely a grass mode, a sand mode, a boulderor rock crawl mode and a mud mode, and also a rough road mode, a towingmode, which in this case is arranged for towing on-road and cantherefore also be considered one of the on-road modes, and an ice mode.The function modes that these vehicle driving modes include are asfollows.

When the vehicle mode controller 98 is in “motorway” mode the vehiclefunctions and subsystem configurations are optimized for traveling athigh speeds on flat surfaces with good levels of friction. Thesuspension ride height is set at “low” for low wind resistance and goodstability. The air suspension interconnection is set at “standard” forgood stability. The steering assistance is set so that it will be low athigh speeds to give a firm steering feel, but will be speed dependentand increase at low vehicle speeds. The brake pedal effort is set at“high” to avoid rapid deceleration at high speed, but with “panicassist” to ensure that the vehicle can be slowed rapidly in anemergency. The A.B.S, E.T.C and D.S.C are all set to “high mu”. Thethrottle progression is set to the “slow” characteristic because this isactually more responsive to changes in throttle pedal position at higherlevels of pedal displacement which will generally be used on a motorway.The transfer box 21 is set to “high range”, the transmission is set to“normal mode” and the center and rear differentials are both “moreopen”.

When the vehicle mode controller 98 is in “country road” mode thefunction settings are the same as for the “motorway” mode, except forthe suspension ride height and the transmission. The suspension rideheight is set to “standard” because reduced wind resistance is lessimportant and the road may be rougher requiring more ground clearanceand more suspension bump travel. The transmission is set to“performance” mode, but the driver has the option of selecting “manual”mode. In an alternative in the country road mode, the throttleprogression is set to “quick” and the brake effort set to “low” so as toassist the driver with rapid acceleration and braking.

When the vehicle mode controller 98 is in “city driving” mode, thefunction settings are again the same as for the “motorway” mode exceptthe suspension ride height and the brake pedal effort. The ride heightis set to standard and the brake pedal effort is set to low to assistthe driver with the rapid and frequent starting and stopping associatedwith city driving. The transmission is set to use relatively high gearssuch as by using the “ice” mode so as to reduce the jerkiness ofdriving, and can even be set to start in second gear rather than firstfor the same reason. The throttle is set to the “slow” mode, again toreduce jerkiness. The throttle pedal characteristic is also set to highdegree of damping, which uses a low-pass filter on the throttle pedalposition signal so that if the pedal is moved quickly, the engine torquedoes not change as quickly. This also helps to reduce jerkiness. In somecases it might be preferred to use the “quick” mode characteristic witha high degree of damping so as to reduce the amount of pedal movementrequired from the driver, but still minimize jerkiness.

When the vehicle mode controller 98 is in “towing” mode, this is assumedto be on-road towing and therefore many of the functions are againsimilar to the other on-road modes. Specifically all of the functionsare at the same settings as in “motorway” mode, except the suspensionride height, the D.S.C., and the transfer box. The ride height is againset to “standard”. The D.S.C. is operated in a special “towing” modewhich is designed to counteract instability brought about by thetrailer. The transfer box 21 is in “high range” since towing willgenerally be carried out on-road. As an alternative to the selection of“high range” the transmission could be operated in a differentconfiguration mode to help the vehicle to manage heavy towed loads. Thiscould be using the “performance” mode which would tend to keep thetransmission in lower gears than normal to help with pulling away underheavy loads. In an alternative towing mode the throttle pedalprogression is set to “quick” so as to help avoid stalling on pull-awayfrom rest.

When the vehicle mode controller 98 is in “dirt track” mode many of thevehicle functions will need to be in different configuration modes fromthe on-road modes described above to take account of the fact that thesurface is rough, although the vehicle might still be traveling at quitehigh speeds, so stability is still important. The ride height is set to“standard”. This is a compromise between being higher to give moresuspension travel to accommodate the rough surface, and being lower forbetter stability. The air suspension interconnection is set to “medium”for good stability. However, if it is assumed that the dirt track willbe very rough the interconnection could be set to “maximum” toaccommodate the rough surface. The steering assistance is set to bespeed dependent as in the motorway driving mode. The brake pedal effortis set to “high” to avoid sudden braking resulting from the jolting ofthe vehicle due to the rough surface. The A.B.S., E.T.C. and D.S.C. areall set to “low mu” because dirt tracks generally have a relatively highamount of loose material on them, and the friction is thereforegenerally quite low. The throttle progression is set to “slow” to avoidthe jolting of the vehicle, and the resulting bouncing of the driver'sfoot on the accelerator pedal from producing undesired changes in thedemanded level of torque. The transfer box 21 is in “high range” becausespeeds will generally be reasonably high. The transmission is in“normal” configuration mode for the same reason. The differential locksare both set to “more open”.

When the vehicle mode controller 98 is in “ice” mode, the functions areset up to provide maximum stability on a slippery surface. The rideheight setting is not critical to this requirement, but is set to“standard” configuration mode for the same reasons as in “dirt track”driving mode. The air suspension interconnection is set to “standard” togive good stability. The steering assistance is set to a low level ofassistance because steering tends to become very “light” on ice andreducing the assistance will reduce the tendency of the driver to changethe steering angle too much and too quickly. The brake pedal effort isset to “high” to avoid sudden braking which might reduce stability. TheA.B.S., E.T.C. and D.S.C. are all set to “low mu” to maintain stability.The throttle progression is set to “slow” to avoid too rapid changes intorque demand which could cause wheel spin. The transfer box 21 is setto high range because speeds might still be relatively high,particularly if the vehicle is being driven on snowy roads. Theautomatic transmission 20 is set to “ice” mode configuration modedescribed above. Both of the differentials are set to “more open” formaximum stability.

‘Grass’ driving mode is similar to ‘ice’ driving mode because both arereasonably flat surfaces with low friction. Therefore many of thefunctions are in similar configuration modes to the “ice” mode. Thedifferences are that the air suspension interconnection is set to“medium” or “maximum” to give better articulation which helps to improvetraction, the transfer box 21 is in “low range” because driving speedswill generally be low on grass, and the center differential 22 is set to“more locked” to improve traction, in particular when climbing anddescending hills. The rear differential 26 could be closed to improvetraction, but this would adversely affect stability under somecircumstances. It can therefore be closed at low speeds, but openincreasingly as speed increases, for example above a threshold of 15 or20 kph, to increase stability.

In “sand” driving mode the functions are the same as for “grass” modeconfiguration modes except the A.B.S., throttle progression andtransmission. The A.B.S. is in the “plough surface” mode describedabove. The throttle progression is set to “quick” and the transmissionis in the specifically designed “sand” mode described above. The E.T.C.is also set to the “sand” mode. The differentials are set to a standardsetting.

In “boulder” driving mode the vehicle will generally be traveling atvery low speeds and the chances of complete loss of traction at one ormore wheels is quite high. The suspension is set to “high” to give goodground clearance. The air suspension interconnection is set to “maximum”to give good articulation. The steering assistance is set to highbecause required steering torques can be high. The A.B.S. is set to“high mu”, although another possibility is to operate the A.B.S. in ade-sensitized mode. In this mode, at least at low speed and when thesteering angle is low, i.e. the driver is steering straight, very highlevels of slip, or even total wheel lock are allowed. However, as thesteering angle increases above a set limit indicating that steering isrequired, wheel lock is again prevented to improve steering control. TheE.T.C. is set to “low mu” because wheel spin is very likely to occur.Another option is to provide a special E.T.C. mode in which the brakesare pre-pressurized either permanently or when high degrees of wheelarticulation are detected, to pre-empt the occurrence of wheel spin. TheD.S.C. is set to “high mu” because it is unlikely that it will be used.Again, another option here is to disable the D.S.C. function altogether,at least below a relatively low threshold speed of, for example, 10 or15 kph. The throttle progression is set to “slow” to give the driver thebest possible control at low speeds. The transfer box 21 is set to “lowrange”. The automatic transmission 20 is set to “manual mode” because itis unlikely that the driver will want to change gear at all, and anyundesired change of gear might affect the stability of the vehicle. Thecenter and rear differentials are both set to “more locked” to give goodtraction.

Finally, in “mud” driving mode the functions are set to the samesettings as in “grass” driving mode, except for the suspension rideheight which is set to “high” to give better clearance over deep mud,and the rear differential 26 which is set to “more locked” to givebetter traction. The air suspension interlock can also be set to“maximum” in order to maximize traction.

A second embodiment of the invention will now be described. In thisembodiment all of the subsystem configurations are substantially thesame as in the first embodiment, the second embodiment differing only inthe manner in which the subsystems configurations are controlled. Someof the controlled functions described above are not altered by thedriving mode selected, and one further function, a hill descentfunction, is included in the brake controller 62, as will be describedin more detail below. The second embodiment will therefore also bedescribed with reference to FIGS. 1 to 4.

In the second embodiment the functions which are controlled by thevehicle mode controller 98 are the throttle pedal characteristic, thegear changes in the transmission 20, the locking torque of the centerand rear differentials 22, 26, the traction control function, the yawcontrol function provided by the D.S.C. system, the air suspension rideheight, the suspension cross linking, and the hill descent controlfunction. The hill descent control defines a target speed and uses thebrakes to control the vehicle speed to the target speed as the vehicledescends a hill. The target speed has a default value which is nominally6 kph, but can be increased by depressing the accelerator pedal 27 anddecreased by depressing the brake pedal down to a minimum value of 3kph. The default target speed can be varied depending on the modeselected. The differential controller 30 is also arranged to receiveinputs from the steering angle sensor 49 and the ride height sensors 83,84, 85, 86, and to vary the locking torque of each of the center andrear differentials 22, 26 in response to those inputs. When highsteering angles are detected the locking torque, in particular of therear differential 26 26, is reduced so as to allow the wheels to rotateat different speeds as is required under cornering. When high levels ofsuspension articulation, indicated by large differences is ride heightsbetween the wheels, is detected, the locking torque is generallyincreased as there is an increased likelihood of wheels slipping.

The driving modes which are selectable in the second embodiment are: astandard mode, a grass/gravel/snow mode, a mud/ruts mode, a sand mode, arock crawl (boulder) mode, and a dynamic mode. The control of thevehicle in each of these modes will now be described.

In the standard driving mode, the configuration modes for the varioussystems are designed to be a compromise that will be suitable for allconditions. The throttle characteristic, gearbox control, tractioncontrol and DSC are set to be suitable for normal on-road driving.Referring to FIG. 7 the throttle characteristic, which relates enginedrive torque to throttle pedal depression, is indicated by curve A whichprovides a steady increase in torque with increasing throttledepression. The differentials are also controlled in a manner suitablefor normal on-road driving. Referring to FIG. 8 the differential lockingtorque is arranged to start at a pre-load level and increase graduallywith slip across the differential as shown in curve A. Referring to FIG.9, the locking torque is also arranged to increase gradually withsuspension articulation as indicated by curve A. The differentialcontroller are also arranged to give a degree of yaw control via therear differential 26. The HDC system is switched off, the suspensionride height is set to standard ride height and the suspension crosslinking is set to its minimum. Referring to FIG. 10, the tractioncontrol is arranged to provide a braking torque to any wheel which isdetected as spinning, the torque starting when the spinning reaches apredetermined threshold level, and increasing gradually with increasingwheel spin as indicated by curve A. Referring to FIG. 11, the D.S.C.system is arranged to provide a steering torque by applying adifferential in braking torque between the two sides of the vehicle.This brake steering torque starts when the yaw error rate, which is thedifference between the expected yaw rate and the measured yaw rate,reaches a predetermined level and increases with increasing yaw errorrate as shown by curve A.

The grass/gravel/snow driving mode is intended for use on grass, graveland snow and other low friction surfaces into which the wheels of thevehicle will not sink to a significant depth. In this driving mode thethrottle characteristic is set to provide a gentle response, that is alow increase in drive torque for any change in throttle pedal positionover most of the range of throttle pedal position, as shown by curve B.At high levels of pedal depression the torque increases at a more rapidrate so that the maximum torque can be achieved at full throttled pedaldepression. This characteristic is arranged to avoid wheel spin bygiving a gentle response within the normal range of throttle pedalpositions. The gearbox control is also arranged to avoid wheel spin, andis therefore arranged to change up gears relatively early, i.e. atrelatively low throttle pedal depressions and engine speeds, and tochange down gears relatively late, i.e. at relatively low engine speeds.The differentials are arranged to have an increased locking torquegenerally, compared to the standard driving mode, as shown by curve B inFIG. 8, so as to reduce the amount of wheel spin which is more likely tooccur on low friction surfaces. The differential controller 30 is alsoarranged to respond more rapidly to detected slipping of thedifferentials, increasing the locking torque more rapidly in response todetected slip of the differentials than in the standard mode. Theresponse of the differentials to suspension articulation is the same asin standard mode. The traction control is arranged to respond morequickly to wheel spin, as shown by curve B in FIG. 10, by brakingspinning wheels more rapidly and therefore allowing less spin than inthe standard mode. The braking starts at lower levels of spin andincreases more rapidly with increasing spin, compared to the standardmode. The engine intervention within the traction control is switched onso as to further reduce the likelihood of wheel spin. The D.S.C. systemis set up as for the standard mode. The hill descent control function isswitched on with a low default target speed of, for example, 3 or 4 kphto improve control of the vehicle when descending hills in slipperyconditions. The suspension ride height is set to standard, and thesuspension cross linking is set to standard since on these surfaces highdegrees of articulation are not expected. Alternatively the crosslinking could be set to medium or even maximum to improve traction,provided the cut-out speed at which the interconnection is closed is lowto avoid loss of stability.

In the mud/ruts driving mode, the throttle characteristic, gearboxcontrol, differential control and stability control are the same is ingrass/gravel/snow driving mode. The traction control is also the sameexcept that the engine intervention is switched off, or at leastminimized. The differential control is the same as for grass/gravel/sanddriving mode, but the sensitivity of the control to changes in steeringangle is reduced since the relatively small amount of wheel slip thatwill result from cornering is less likely to cause a loss of tractionthan is the spinning of one of the wheels due to a loss of grip.Specifically referring to FIG. 12, the differential control includes aturning factor which starts to decrease the locking torque when thesteering angle increases above 120° and reduces the locking torque tozero when the steering angle reaches 200°. This is to prevent thedifferentials from inhibiting cornering. In the mud/ruts driving modethe reduction in locking torque in response to turning is reducedbecause maintaining traction takes a higher priority than accuratesteering under those conditions. The D.S.C. system is de-sensitized asshown by curve B in FIG. 11. The hill descent control is switched onwith the standard default target speed of 6 kph to provide maximumcontrol on hills, the suspension ride height is set to the high settingso as to increase ground clearance, which is desirable in deep mud andruts, and the suspension cross linking is set to the maximum setting tomaximize traction.

In the sand driving mode, the subsystem configuration modes are set upfor driving on sand, and in particular to provide the best traction onsand. The throttle characteristic is as shown by curve C in FIG. 7, andis arranged to be relatively gentle at low degrees of throttle pedaldepression so as to reduce the chances of wheel spin at low speeds.Therefore at low degrees of pedal depression the torque produced islower, for any given pedal position, than in the standard mode. Howeverat high degrees of throttle pedal progression the drive torque demandincrease more rapidly with throttle pedal depression so as to producemore power more quickly than in the standard mode. Therefore at highdegrees of throttle pedal depression the torque produced for any givenpedal position is higher than in the standard mode. Similarly thetransmission control operates in the sand mode described above in thefirst embodiment. The differential control is the same as in themud/ruts mode, again having a low sensitivity to steering angle for thesame reason. The traction control system is set up to allow higherlevels of wheel spin than in the standard mode as shown by curve C inFIG. 10. As an alternative to this the traction control may use aspecial sand mode configuration as described above for the firstembodiment in which wheel spin is kept very low at low vehicle speeds,but is allowed to increase to relatively high levels at higher vehiclespeeds. The engine intervention is switched off to prevent undesirablereductions in drive torque. The D.S.C. system is set to a lowsensitivity as shown by curve C in FIG. 11, brake steer torque beingintroduced only at high levels of yaw rate error and increasing slowlywith increasing yaw rate error. As an alternative the D.S.C. system canbe turned off altogether in sand mode. The hill descent control isswitched off because sand generally provides a high degree of drag andthe vehicle either needs to be driven positively down a hill rather thanbraked, or, if braking is required, engine braking is generallysufficient. The suspension ride height is set to standard height and thesuspension cross linking is set to minimum.

In the rock crawl driving mode the throttle characteristic is set, as ingrass/gravel/snow and mud/ruts driving modes, to follow curve B in FIG.7, i.e. to be relatively insensitive to changes in throttle pedalposition over the range of positions usually used. Gearbox control isalso set up as for grass/gravel/snow and mud/ruts driving modes. Thedifferentials are set up to follow curve B in FIG. 8, i.e. to have ahigher starting locking torque than in grass/gravel/snow and mud/rutsdriving modes, and to increase the locking torque more rapidly inresponse to differences in wheel speeds between the vehicles wheels, asmeasured by slip across the differentials. The response of thedifferential control to suspension articulation is also increased asshown by curve B in FIG. 9, with the rate of change of locking torquewith increasing articulation being higher than in the standard mode. Thetraction control and D.S.C. are set up as in the mud/ruts mode, thetraction control following curve B in FIG. 10 to provide an increasedsensitivity to wheel spin, and the D.S.C. following curve B in FIG. 11to provide a decreased sensitivity to yaw rate error. The hill descentcontrol is switched on with a low default target speed of, for example 3kph, the suspension ride height is set to high to give best groundclearance and the suspension cross linking is set to maximum to allowmaximum suspension articulation.

As an alternative, an improved rock crawl driving mode may be includedin which the subsystem configuration modes are selected to achieve andmaintain the requested vehicle speed. The engine controller 28 in theform of an engine management system controls operation of the engine 18so as to control its speed and output power and torque in response todriver inputs. The driver inputs may be in the form of the traditionalcruise control switches, or preferably via the accelerator pedal. Theengine controller 28 will operate as a torque controller and willdetermine the error between actual road speed and the requested roadspeed demanded by the driver. This error will then be managed by theengine controller 28. One alternative for managing the error wouldconsist of a proportional, integral and differential term strategy. Theengine controller 28 will be optimized to enable the requested roadspeed to be achieved and maintained, using up to maximum availabletorque while providing comfort and predictability to the driver. Asshown in FIG. 7, the accelerator pedal will allow large throttlemovement resulting in small requested changes in road speed. This willhelp to alleviate the movement of the driver's foot caused by thesometimes-violent movement of the vehicle over rough terrain. As theaccelerator pedal moves toward full travel, it may transfer from avehicle speed controller to a torque controller, to enable the driver toaccelerate at a higher rate. AT zero pedal position, the road speedrequest will be zero to provide maximum engine braking and idle.

The improved rock crawl mode may also include an improved Hill Descentcontrol system. In the event in which the brakes are used to controlroad speed where maximum engine braking has been reached but the roadspeed is still higher than the requested driver input speed, the hilldescent control would control to a specific road speed or zero roadspeed if the throttle were closed.

Finally, a dynamic driving mode is included which is intended for moresporty driving. In this mode the throttle pedal characteristic followscurve D in FIG. 7, being arranged to produce the most engine torque forany given throttle pedal position, and the most rapid increase in enginetorque in response to throttle pedal depression, over the lower range ofthrottle pedal depressions. The gearbox control is also arranged to keepthe gearbox in lower gear then in the standard mode, with the changes upbeing delayed when the vehicle is accelerating and changes down beingmade early when the vehicle is slowing, so as to give the bestacceleration and the most engine braking on deceleration. The tractioncontrol and D.S.C and differentials are set to the same settings as instandard driving mode, the suspension is set to its lowest ride height,and the hill descent control is turned off.

Referring to FIG. 13, in a third embodiment of the invention the drivingmode in which the vehicle operates is determined by two separate inputs.One input, a rotary terrain knob 100, allows the user to input the typeof terrain over which the vehicle is being driven. The other input, arotary “mode of use” knob 102 allows the user to input the mode in whichthe vehicle is to be used. This can include vehicle modes relating tothe manner in which the vehicle is to respond to the driver's inputs,such as a sport mode or an economy mode, as well as modes relating tothe state of the vehicle, such as a towing mode suitable for towing atrailer, and a laden mode for when the vehicle is carrying aparticularly heavy load. In this example the vehicle “mode of use” knoballows selection of normal, sport, and towing vehicle driving modes. Thesport driving mode is adapted for use when the vehicle is being drivenin a “sporty” manner, characterized for example by one or more of: rapidacceleration and braking, high cornering speeds, high engine speeds andrelatively low gears for any given vehicle speed.

The terrain selection input allows the selection of standard,grass/gravel/snow, mud/ruts, sand, and rocks driving modes as in thesecond embodiment. When the “mode of use” input is set to normal theoperating modes of the vehicle correspond to the driving modes in thesecond embodiment. If the mode-of-use input is turned to towing mode,then each of the terrain modes selected is modified to make the vehiclemore effective at towing. For example, the suspension ride height islocked, or changes in height restricted, so as to avoid tilting thetrailer, and the throttle map and gear change map are modified so as toprovide a high level of torque when pulling away from rest. When thesport mode-of-use is selected, the subsystem configuration modes arecontrolled so as to provide a sporty driving feel: the suspension islowered, the throttle map and gear change maps are modified to providerapid acceleration and high levels of engine braking.

In some terrains, one or more of the mode-of-use selections may beinappropriate and selection of those modes-of-use may not result inmodification of the vehicle control when those terrains are selected.For example the sport mode-of-use may not be selectable, or may have noeffect on the vehicle, of selected in combination with rock crawl,mud/ruts or grass/gravel/snow. Towing is, however, selectable with allterrain selections.

Referring to FIG. 14 a vehicle according to a fourth embodiment of theinvention has a powertrain similar to that of the first embodiment andshown in FIG. 1, and corresponding parts are indicated by the samereference numeral increased by 100. The difference between thisembodiment and the first is that the center differential is replaced bya power take off system 122 which includes a direct coupling 122abetween the transfer box 121 and the front differential 124, and aclutch mechanism 122b which can be controlled by the powertraincontroller 130 to redirect drive torque to the rear differential 126 andhence to the rear wheels 113 114. Under normal driving conditions theclutch mechanism 122b allows substantially all of the driving torque tobe transmitted directly to the front wheels via the front differential124. However, if the front wheels start to slip, as detected for exampleby wheel speed sensors, then the clutch mechanism 122b is operated todirect drive torque to the rear wheels 113, 114 via the reardifferential 126. The proportion of the drive torque which isre-directed to the rear differential 126 is controlled so as to reducethe amount of slip at the front wheels to an acceptable level. Theclutch 122b is set to a pre-load which is variable, and the clutch loadis then increased in response to detected slip of the front wheels 111,112. In situations where good traction is required, a high pre-load andhigh sensitivity to slip are desirable. For good dynamic performance alow re-load is desirable and sensitivity to slip is less important. Foron-road driving, low pre-load and sensitivity are provided, and foroff-road driving a higher pre-load and higher sensitivity are provided.If a sand mode is provided the degree of slip is set to be low at lowspeeds and higher at higher speeds in a similar manner to the tractioncontrol system.

Referring to FIG. 15, the fourth embodiment also includes, as well assprings 176 in its suspension system, dampers 177 arranged to dampvertical movement of the wheels 111 relative to the vehicle's body 115.The dampers 177, only one of which is shown, are electricallycontrolled, having a variable damping rate, which is variable between ahigh level, where relatively high resistance is provided to verticalwheel travel, and a lower rate at which less resistance is provided. Thedamping of each of the dampers 177 is controlled by the suspensioncontroller 182. The damping can be controlled in response to a number ofparameters such as vehicle speed and steering angle to improve ride andhandling. The amount of damping is also varied depending on which modeis selected. In on-road modes a high degree of damping is generallyprovided to give good handling, and in off-road modes lower damping isprovided to give good traction.

In this fourth embodiment, the vehicle mode controller 98 usesinformation passed on from the various subsystem controllers relating tothe nature of the surface over which the vehicle is traveling, themanner in which the vehicle is being driven, and the way in which thevehicle is being used, to select an appropriate mode automatically. Forexample, the wheel speed sensors and ride height sensor are used toclassify the nature of the surface as on-road or off-road, high frictionor low friction, etc. The powertrain controller 130 and steering anglesensor 49 are used to classify the driving style as normal or sporty. Itis also possible to determine from the various sensors whether thevehicle is heavily laden.

The automatic mode selection can either be the sole means of selectingmodes, giving the driver no input to the mode selection process.Alternatively it may be advisory, with the driving having the option tooverride the automatic selection of mode. In a further alternative thedriver may have the primary control over the selection of the drivingmode, with the vehicle mode controller 98 over-riding the driver'sselection if the driving conditions or driving style of the driver makethe driver's selection unsafe.

It will be appreciated that the number of available modes can be varieddepending on the requirements for a particular vehicle. For example inthe simplest case, it might be that only two modes were required, whichmight be the standard mode which would be suitable for “on-road” drivingand the rock crawl mode which would be suitable for “off-road driving”.Alternatively, there could be one on-road mode and two off-road modes,for example the rock crawl mode and the grass/gravel/snow mode.

Having thus described the invention of the present application in detailand by reference to preferred embodiments thereof, it will be apparentthat modifications and variations are possible without departing fromthe scope of the invention defined in the appended claims.

What is claimed:
 1. A vehicle control system having a driver input forselecting a driving surface, the vehicle control system arranged tocontrol a plurality of vehicle subsystems each of which is operable in aplurality of subsystem configuration modes, wherein the vehicle controlsystem is operable in a plurality of driving modes in each of which itis arranged to select the subsystem configuration modes in a mannersuitable for a respective driving surface.
 2. A vehicle control systemaccording to claim 1, wherein the driving modes comprise a plurality ofdifferent driving modes suitable for different conditions of thevehicle.
 3. A vehicle control system according to claim 1 wherein thedriving modes include an off-road mode in which the subsystemconfigurations are controlled in a manner suitable for driving on roughterrain and an on-road mode in which the subsystem configurations arecontrolled in a manner suitable for driving on-road.
 4. A vehiclecontrol system according to claim 1 wherein the driving modes include atleast one low friction mode in which the subsystem configurations arecontrolled in a manner suitable for driving on low friction surfaces anda high friction mode in which the subsystem configurations arecontrolled in a manner suitable for driving on high friction surfaces.5. A vehicle control system according to claim 4 wherein the lowfriction mode is arranged to be suitable for driving on grass, graveland snow.
 6. A vehicle control system according to claim 1 wherein thedriving modes are selectable by a driver of the vehicle.
 7. A vehiclecontrol system according to claim 6 wherein the driving modes areselectable by means of two inputs, one of which is a terrain selectioninput arranged to influence the configuration mode selected on the basisof the terrain selected, and the other which is a mode of use inputarranged to influence the configuration mode selected on the basis of aselected mode of use of the vehicle.
 8. A vehicle control systemaccording to claim 6 wherein the mode of use input is arranged to allowselection between a plurality of driving styles.
 9. A vehicle controlsystem according to claim 8 wherein the driving style includes a sportstyle.
 10. A vehicle control system according to claim 1 furthercomprising sensing means arranged to sense at least one parameterwherein the control system is arranged to select said driving modes onthe basis of said parameter.
 11. A vehicle control system according toclaim 10 wherein the parameter varies with the manner in which thevehicle is being used.
 12. A vehicle control system according to any oneof claims 1-11 in which the vehicle control system is further includedin a motor vehicle.
 13. A vehicle control system according to claim 1further comprising a driver input for selecting a mode of use.
 14. Amethod of controlling a plurality of subsystems within a motor vehiclein a manner suitable for a respective driving surface, the subsystemseach being operable in a plurality of subsystem configuration modes, themethod comprising the steps of: connecting a vehicle mode controller tothe vehicle subsystems, the vehicle mode controller having a pluralityof driving modes and a driver input for selecting a driving surface;storing a set of control commands from the plurality of driving modes ina memory of the vehicle mode controller in response to the driver inputof a driving surface; transmitting the set of stored control commands toeach of the plurality of vehicle subsystems; and selecting of a set ofsubsystem control parameters by each of the plurality of vehiclesubsystems so as to provide the appropriate operation of each of thevehicle subsystems.
 15. The method claimed in claim 14, wherein at leastone of the driving modes is a rock crawl mode.
 16. A method ofcontrolling a plurality of subsystems within a motor vehicle in a mannersuitable for a respective driving surface, the subsystems each beingoperable in a plurality of subsystem configuration modes, the methodcomprising the steps of: connecting a vehicle mode controller to thevehicle subsystems, the vehicle mode controller having a plurality ofdriving modes, a driver input for selecting a driving surface, and aplurality of subsystem sensor information; storing a set of controlcommands from the plurality of driving modes in a memory of the vehiclemode controller in response to the plurality of subsystem sensorinformation and the driver input of the driving surface; transmittingthe set of stored control commands to each of the plurality of vehiclesubsystems; and selecting of a set of subsystem control parameters byeach of the plurality of vehicle subsystems so as to provide theappropriate operation of each of the vehicle subsystems.
 17. A computerprogram product comprising a medium on which or in which, when executedin a computer system, will perform the method as in any one of claims14-16.
 18. A vehicle control system having a driver input for selectinga surface terrain, the vehicle control system arranged to control aplurality of vehicle subsystems each of which is operable in a pluralityof subsystem configuration modes, wherein the vehicle control system isoperable in a plurality of driving modes in each of which it is arrangedto select the subsystem configuration modes in a manner suitable for arespective surface terrain.
 19. A vehicle control system according toclaim 18, wherein one of the plurality of vehicle subsystems is asuspension subsystem.
 20. A vehicle control system according to claim19, wherein the plurality of vehicle subsystems further comprise asteering subsystem, a brake subsystem, an engine management subsystem,and a transmission subsystem.
 21. A vehicle comprising a vehicle controlsystem having a driver input device for selecting a driving surface, thevehicle control system arranged to control a plurality of vehiclesubsystems each of which is operable in a plurality of subsystemconfiguration modes, wherein the vehicle control system is operable in aplurality of driving modes in each of which it is arranged to select thesubsystem configuration modes in a manner suitable for a respectivedriving surface, and further wherein the plurality of driving modesincludes at least two off-road modes in which the subsystemconfigurations are controlled in a manner suitable for driving onrespective off-road driving surfaces, and still further wherein one ofthe off-road modes is a mode in which the subsystems are controlled in amanner suitable for driving on rocks and/or boulders.
 22. A vehicle asclaimed in claim 21, wherein one of the vehicle subsystems is a brakesubsystem and wherein, in the mode suitable for driving on rocks and/orboulders, the subsystem configuration modes are arranged such that whenthe steering angle is below a predetermined threshold, higher levels ofwheel slip are permitted than when the steering angle is above thepredetermined threshold and/or total wheel lock is permitted.
 23. Avehicle as claimed in claim 21, wherein one of the vehicle subsystems isa brake subsystem and wherein, in the mode suitable for driving on rocksand/or boulders, the subsystem configuration modes are arranged suchthat the brakes are pre-pressurized either permanently or in dependenceon detection of wheel articulation.
 24. A vehicle control system havinga driver input device for selecting a driving surface, the vehiclecontrol system arranged to control a plurality of vehicle subsystemseach of which is operable in a plurality of subsystem configurationmodes, wherein the vehicle control system is operable in a plurality ofdriving modes in each of which it is arranged to select the subsystemconfiguration modes in a manner suitable for a respective drivingsurface, wherein one of the plurality of vehicle subsystems is asuspension subsystem and said plurality of subsystem configuration modescomprises a plurality of ride heights; wherein one of the plurality ofvehicle subsystems is a powertrain system which includes a powertraincontrol means and a throttle pedal, the subsystem configuration modesproviding different levels of responsiveness of the powertrain controlmeans to movement of the throttle pedal; wherein one of the plurality ofvehicle subsystems is a steering system which can provide steeringassistance, and said plurality of subsystem configuration modes providesdifferent levels of steering assistance; and wherein one of theplurality of vehicle subsystems is a transmission system operable in aplurality of transmission ratios and including a transmission controlmeans arranged to monitor at least one parameter of the vehicle and toselect the transmission ratios in response, and wherein the subsystemconfiguration modes include a plurality of transmission configurationmodes in which the transmission ratios are selected differently inresponse to said at least one parameter.
 25. A vehicle comprising avehicle control system having a driver input device for selecting adriving surface, the vehicle control system arranged to control aplurality of vehicle subsystems each of which is operable in a pluralityof subsystem configuration modes, wherein the vehicle control system isoperable in a plurality of driving modes in each of which it is arrangedto select the subsystem configuration modes in a manner suitable for arespective driving surface, and further wherein the plurality of drivingmodes includes at least two off-road modes in which the subsystemconfigurations are controlled in a manner suitable for driving onrespective off-road driving surfaces, and an on-road mode in which thesubsystem configurations are controlled in a manner suitable for drivingon-road, and still further wherein the subsystem configuration modes arearranged such that the vehicle adopts a higher ride height in dependenceon selection of the second off-road mode than for the first off-roadmode, and yet still further wherein one of the plurality of vehiclesubsystems is a transmission system operable in a plurality oftransmission ratios and including a transmission control means arrangedto monitor at least one parameter of the vehicle and to select thetransmission ratios in response, and wherein the subsystem configurationmodes include a plurality of transmission configuration modes in whichthe transmission ratios are selected differently in response to said atleast one parameter.
 26. A vehicle as claimed in claim 25, wherein thesubsystem configuration modes are arranged such that in the secondoff-road mode, the transmission is kept in a higher gear than in theon-road mode at low vehicle speeds but uses lower gears than in theon-road mode at higher vehicle speeds.
 27. A vehicle as claimed in claim21, wherein one of the vehicle subsystems is a steering subsystem whichcan provide steering assistance, and wherein, in the mode suitable fordriving on rocks and/or boulders, the steering subsystem is set toprovide a high level of steering assistance relative to the on-road modeand/or the other off-road mode.
 28. A vehicle as claimed in claim 21,wherein one of the vehicle subsystems is a brake subsystem, and wherein,in the mode suitable for driving on rocks and/or boulders, the brakesubsystem is arranged to require low brake pedal effort relative to theon-road mode and/or the other off-road mode.
 29. A vehicle as claimed inclaim 21, wherein one of the vehicle subsystems is a transfer box, andwherein, in the mode suitable for driving on rocks and/or boulders, thetransfer box is set to low range.
 30. A vehicle as claimed in claim 29,wherein one of the vehicle subsystems is an automatic transmission, andwherein, in the mode suitable for driving on rocks and/or boulders, theautomatic transmission is set to a manual mode.
 31. A vehicle as claimedin claim 30, wherein one of the vehicle subsystems is an air suspensionsystem, and wherein, in the mode suitable for driving on rocks and/orboulders, the suspension is set to a high ride height relative to theon-road mode and/or other off-road mode.
 32. A vehicle as claimed inclaim 21, wherein one of the vehicle subsystems is an electronictraction control system, and wherein, in the mode suitable for drivingon rocks and/or boulders, the electronic traction control subsystem isset to low mu.
 33. A vehicle as claimed in claim 21, wherein one of thevehicle subsystems is an electronic traction control system and anotherone of the vehicle subsystems is a brake subsystem, and wherein, in themode suitable for driving on rocks and/or boulders, the brakes arepre-pressurized in dependence on detection of wheel articulation.
 34. Avehicle control system having a driver input device for selecting adriving surface, the vehicle control system arranged to control aplurality of vehicle subsystems each of which is operable in a pluralityof subsystem configuration modes, wherein the vehicle control system isoperable in a plurality of driving modes in each of which it is arrangedto select the subsystem configuration modes in a manner suitable for arespective driving surface, and further wherein the plurality of drivingmodes includes at least two off-road modes in which the subsystemconfigurations are controlled in a manner suitable for driving onrespective off-road driving surfaces, and an on-road mode in which thesubsystem configurations are controlled in a manner suitable for drivingon-road, and still further wherein one of the off-road modes is a sandmode in which the vehicle subsystems are controlled in a manner suitablefor driving on sand, wherein one of the vehicle subsystems is a brakesubsystem and wherein, in the sand mode, the brake subsystem is arrangedto allow a high degree of wheel slip under braking relative to theon-road mode and/or a second off-road mode.
 35. A vehicle control systemhaving a driver input device for selecting a driving surface, thevehicle control system arranged to control a plurality of vehiclesubsystems each of which is operable in a plurality of subsystemconfiguration modes, wherein the vehicle control system is operable in aplurality of driving modes in each of which it is arranged to select thesubsystem configuration modes in a manner suitable for a respectivedriving surface, wherein the system comprises a plurality of subsystemsensors and wherein the system is operable in an automatic selectionmode in which one of the plurality of driving modes is selectedautomatically in dependence on subsystem sensor information.
 36. Avehicle control system according to claim 35, wherein the plurality ofsubsystem sensors comprises one or more of a wheel speed sensor, a rideheight sensor and a steering angle sensor.
 37. A vehicle control systemhaving a driver input device for selecting a driving surface, thevehicle control system arranged to control a plurality of vehiclesubsystems each of which is operable in a plurality of subsystemconfiguration modes, wherein the vehicle control system is operable in aplurality of driving modes in each of which it is arranged to select thesubsystem configuration modes in a manner suitable for a respectivedriving surface, wherein the system comprises a plurality of subsystemsensors and wherein the system is operable to determine an appropriatedriving mode from the plurality of driving modes for the current drivingconditions and to output advice to the driver relating to the determineddriving mode.
 38. A vehicle control system having a driver input devicefor selecting a driving mode, the vehicle control system arranged tocontrol a plurality of vehicle subsystems each of which is operable in aplurality of subsystem configuration modes, wherein the vehicle controlsystem is operable in a plurality of driving modes in each of which itis arranged to select the subsystem configuration modes in a mannersuitable for a respective driving surface, wherein one of the pluralityof vehicle subsystems is a suspension subsystem and said plurality ofsubsystem configuration modes comprises a plurality of ride heights; andwherein one of the plurality of vehicle subsystems is a powertrainsystem which includes a powertrain control means and a throttle pedal,the subsystem configuration modes providing different levels ofresponsiveness of the powertrain control means to movement of thethrottle pedal.
 39. A vehicle control system according to claim 38,wherein one of the subsystems comprises a traction control system whichis arranged to control wheel spin, and said plurality of subsystemconfiguration modes allow different levels of said wheel spin.
 40. Avehicle control system according to claim 38, wherein one of theplurality of vehicle subsystems is a steering system which can providesteering assistance, and said plurality of subsystem configuration modesprovides different levels of steering assistance.
 41. A vehicle controlsystem according to claim 38, wherein one of the plurality of vehiclesubsystems is a transmission system operable in a plurality oftransmission ratios and including a transmission control means arrangedto monitor at least one parameter of the vehicle and to select thetransmission ratios in response, and wherein the subsystem configurationmodes include a plurality of transmission configuration modes in whichthe transmission ratios are selected differently in response to said atleast one parameter.
 42. A vehicle control system according to claim 38,wherein one of the subsystems is a brake system which can provide ananti-lock function to control wheel slip, and said plurality ofsubsystem configuration modes allow different levels of said wheel slip.43. A vehicle control system according to claim 38, wherein theplurality of driving modes includes at least two on-road modes in whichthe subsystem configurations are controlled in a manner suitable fordriving on-road.
 44. A vehicle control system according to claim 43,wherein one of the on-road modes is a dynamic mode or a sport mode. 45.A vehicle control system according to claim 44 where one of the on-roadmodes is a standard mode or a default mode.
 46. A vehicle control systemaccording to claim 44 where one of the on-road modes is an economy mode.47. A vehicle control system according to claim 44 wherein one of theon-road modes is a motorway mode or a country road mode.
 48. A vehiclecontrol system according to claim 38 wherein the plurality of drivingmodes includes an off-road mode in which the subsystem configurationsare controlled in a manner suitable for driving on grass, or an off-roadmode in which the subsystem configurations are controlled in a mannersuitable for driving on gravel, or an off-road mode in which thesubsystem configurations are controlled in a manner suitable for drivingon snow, or an off-road mode in which the subsystem configurations arecontrolled in a manner suitable for driving on rocks, or an off-roadmode in which the subsystem configurations are controlled in a mannersuitable for driving on sand or an off-road mode in which the subsystemconfigurations are controlled in a manner suitable for driving on mud.49. A vehicle control system according to claim 43, wherein theplurality of driving modes includes an off-road mode in which thesubsystem configurations are controlled in a manner suitable for drivingon gravel and wherein, in the off-road mode suitable for driving ongravel, the powertrain system is arranged to provide lower levels ofdrive torque, for a given throttle pedal position, than in at least oneof the on-road modes.
 50. A vehicle control system according to claim43, wherein the plurality of driving modes includes an off-road mode inwhich the subsystem configurations are controlled in a manner suitablefor driving on gravel and wherein, in the off-road mode suitable fordriving on gravel, the suspension system is arranged to provide a higherride height than in at least one of the on-road modes.
 51. A vehiclecontrol system according to claim 50, wherein, in the off-road modesuitable for driving on gravel, the powertrain system is arranged toprovide lower levels of drive torque, for a given throttle pedalposition, than in at least one of the on-road modes.
 52. A vehiclecontrol system according to claim 38, wherein the driving modes areselectable by means of two separate driver input devices.
 53. A vehiclecontrol system according to claim 52, wherein one of the driver inputdevices is a terrain selection input arranged to select the driving modeon the basis of the terrain selected and the other driver input deviceis a mode of use input.
 54. A vehicle control system according to claim53, wherein the plurality of driving modes includes at least two on-roadmodes in which the subsystem configurations are controlled in a mannersuitable for driving on-road, wherein at least one of the on-road modesis a sport mode or an economy mode selectable by the mode of use input.55. A vehicle control system according to claim 53, wherein theplurality of driving modes includes at least one off-road mode in whichthe subsystem configurations are controlled in a manner suitable fordriving on at least one of grass, gravel, snow, rocks, sand or mud,wherein the at least one off-road mode is selectable by the terrainselection input.
 56. A vehicle control system according to claim 55,wherein the plurality of driving modes includes at least two on-roadmodes in which the subsystem configurations are controlled in a mannersuitable for driving on-road, wherein at least one of the on-road modesis a sport mode or an economy mode selectable by the mode of use input.57. A vehicle control system having a driver input device for selectinga driving mode, the vehicle control system arranged to control aplurality of vehicle subsystems each of which is operable in a pluralityof subsystem configuration modes, wherein the vehicle control system isoperable in a plurality of driving modes in each of which it is arrangedto select the subsystem configuration modes in a manner suitable for arespective driving surface, wherein one of the plurality of vehiclesubsystems is a suspension subsystem and said plurality of subsystemconfiguration modes comprises a plurality of ride heights; and whereinone of the plurality of vehicle subsystems is a powertrain system whichincludes an engine and a throttle pedal, the subsystem configurationmodes providing different amounts of torque from the engine for a giventhrottle pedal position.
 58. A vehicle comprising a vehicle controlsystem according to any one of claims 24, 34, 35, 37, 38 and 57.